Permanent magnet motors can generally be divided into permanent magnet synchronous motors (PMSMs) and brushless DC motors (BLDCMs) according to air-gap magnetomotive force (MMF) and operating current waveforms. PMSM type motors have attracted increasing attention and usage due to its relatively high control precision, high torque density, good torque stability, and low noise. During the control procedure of permanent magnet synchronous motors, a driving torque for motors produced by a sinusoidal control current can be substantially smooth, so as to improve the torque control performance of motors and to significantly decrease running and starting noise. Therefore, the operating or “stator” current may be required to be sinusoidal current during operation of permanent magnet synchronous motors.